As an example, rice breeding went through two revolutionary breakthroughs of semi-dwarfication and hybrid breeding in history. The semi-dwarfication breeding of rice was first started by Chinese academician Yaoxiang Huang from the Rice Research Institute of Guangdong Academy of Agricultural Sciences of China and breeders in other parts of the world. The hybrid rice breeding was invented by Chinese academician Longping Yuan, ‘the father of hybrid rice’. These two events promoted the rice breeding of China to a leading position in the world. Up to now, the production of rice and other crop plants has nevertheless been dominated by single genotype varieties, which share one single genotype for all their plants within a certain variety. The development and release of single-genotype varieties directly resulted in an increasing reduction of genetic diversity. Single-genotype varieties became increasingly narrow in genetic backgrounds and became increasingly weak in the resistance and tolerance to diseases and biological natural enemies, resulting in the prevalence of various diseases in the past, such as rice helminthosporium leaf spot, potato blight, wheat strip rust, Southern leaf blight (Bipolaris maydis) and Northern leaf blight (Setosphaeria turcica) in maize, and recent outbreak of locusts in some African regions. The infall of rust disease of soybean in the United States in 2004 brought about a high panic. According to a report of a meeting for World Cereal Day in 4 Oct., 2004, three fourths of the genes in agricultural plants vanished in the last century, and things are getting still worse at present.
Hybrid rice also belongs to a single genotype category. In addition, the problem of seed impurity in the production and multiplication of hybrid rice would occur more or less every year due to the instability of their sterile lines. A case of example is the complete failure of production of hybrid rice seeds in an around 3000 hectares of lands in Guangdong province of China in 2005. The cause of the failure was the sensibility to cold dew wind due to spraying of giberrelin 920 during hybrid seeds production. Due to its high social and research costs and high technical risks, hybrid rice has not been commercialized in large scale in United States and other countries. In China, the production of hybrid rice has been increasing very fast with the country's rapid development of market-oriented economy. One of the important reasons is that the enforcement of plant variety rights is still incomplete in the country, and in particular, the conventional varieties cannot be well protected. As a result, the seed enterprises are only willing to produce and sell hybrid seeds rather than conventional variety seeds, as they are able to dominate on the seed market through a control of the production of hybrid seeds which is characterized with high cost and risk. The economical interests of seed companies played an important role for extension of hybrid rice. For the heterosis utilization in other crop plants, the cost is also very high for developing sterile lines and making two-line or three-line combinations. The application of chemical emasculation method of hybrid seeds production is badly restricted by climatological factors and other technical problems and it will cause chemical pollution and other environmental problems.
High yielding, high quality and multiple resistances to pests and diseases are always the targets of crop breeding, but it is hard to conciliate these three goals for a single-genotype variety and it is getting increasingly difficult for a single-genotype variety to exceed in all aspects. Briefly speaking, for the traditional crop breeding or single-genotype breeding, breeders attempt to select desirable and perfect individuals and it is unavoidable to attend to one thing and lose another.
The inventor Xiaofang Li has previously created a new breeding strategy for crop plants, which was called multi-genotype (colony variety) breeding or genetic diversity breeding. She has ever applied a patent for it and the application number was PCT/CN2004/000657. The core of this breeding strategy is to create and form an elite group instead of desirable individuals in crop plants. It has made major innovation in the concept, strategy, tactic, selection criteria of breeding in crop plants. It focuses on the coordination in yield, quality and resistance to pests and diseases of crop plants. It will facilitate the active protection and utilization of genetic diversity of crop plants in agriculture. The multi-genotype (colony variety) breeding is a specialized term. Judged by its goal, it can be called genetic diversity breeding. The multi-genotype (colony) variety can be generally called group variety for the sake of farmers in understanding.
The multi-genotype (colony variety) breeding includes the following seven phases. (1) Selection of parental lines: According to the breeding targets, the male and female parents with many excellent agronomical traits or some special characteristics will be chosen. It's unnecessary for a pair of male and female parents to supplement mutually in traits. However, all the parental lines should supplement collectively and the balance in their traits should also be considered for the breeding targets. The parental lines should vary according to the breeding goal. For instance, more parental lines with high quality should be chosen for quality breeding, and more resistant parental lines should be adopted for resistance and tolerance breeding. (2) Hybridization: Maximum number of recombinants should be created at the minimum cost of hybridization. For instance, composite or piled-up hybridization, in which pairs of parental lines are crossed for the first time and pairs of F1 are subsequently crossed once more, will greatly reduce the workload of hybridization and large quantity of recombinants can be acquired in a short time. (3) Self-crossing for segregation and recombination: It can be easily realized for self-pollinating or often-cross-pollinating crop plants. In this phase, all family lines of hybridization should be retained possibly and certain number of plants should be kept for each family line according to the multiplication capability of the plants. A single-seed-descent selection should be conducted for all family lines. Each family line should not be totally eliminated too early so that the genetic diversity can be maintained in all these family lines. According to breeder's experience, the poor plants can be deleted from a family line after several generations of self-crossing. (4) Characterization of individual plant lines: After all family lines become stable, each individual plant line will be evaluated for selection. After the poor plant lines are eliminated, the other plant lines will constitute the fundamental population and their major characteristics will be determined or measured. The indices to be investigated will depend on facilities and time allowance. The growth duration and plant height must be investigated, for they indicate the uniformity of a variety. (5) Grouping and assortment: The data for characteristics in the fundamental population are put in the computers for analysis. The individual plant lines which are identical in growth duration and plant height and share a common breeding goal are merged in a group to become a colony variety. Couples or even dozens of colony varieties can be developed from a fundamental population according to growth duration, plant height and breeding goals. (6) Improvement of colony varieties: The individual plant lines of a colony variety are grown in separate rows in the same plot of a field to examine the data for accuracy in measurement or computer input. The inconsistent plant lines or lines with obvious inaccuracy in data are deleted to ensure a whole uniformity in a plot. This process can be repeated for more than one generation for a multilevel improvement of a colony variety. (7) Formation of multi-genotype colony varieties: The original plant lines of a colony variety in the fundamental population can be regarded as breeder seed. Their corresponding plant lines are multiplied separately and their seeds are mixed in a specific ratio to form a multi-genotype colony variety or group variety. Then normal regional trials like that for conventional breeding are conducted subsequently. The seeds of the fundamental population formed in the fourth phase are equivalent to breeder seeds, and those of the original plant lines formed in the sixth phase are the stock seeds of colony varieties. As individual plant lines are different in their multiplication capacity, farmers won't be able to reserve the seeds for planting for a long time. The seeds companies will be able to produce the seeds properly and keep their plants stable and unchangeable in characteristics. In case farmers reserve the seeds for planting temporally, serious risk of sterility caused by sterile lines won't take place. For those crop plants which are easy in hybrid seed production with no need of sterile lines, the hybrid F1 can be used as fundamental populations and multi-genotype hybrid combinations or a mixture of colony variety and combination can be constructed from them. Figuratively speaking, conventional single-genotype breeding tends to be a process of selecting beauideal individuals while multi-genotype breeding is a course to seek an elite group.
The main advantage of genetic diversity breeding is that it is as easy as conventional breeding in technical difficulty but its cost for seed production is much lower than hybrid combinations. In addition, it avoids the risk of sterility caused by sterile lines. Thus it is a low-cost and zero-risk technology. This technology can be effectively protected by law through application of patent and the interests of seed enterprises can be also guaranteed. It can promote the industrialization of seeds of crop plants and enhance the core competitiveness in agriculture. Right now, the protection of bio-diversity is a hot topic and focus of public attention around the world. This technology will also boost the protection of bio-diversity and promote the sustainable development in agriculture.